An industrial need exists for a low cost, high torque-to-weight ratio, brushless electrical motor capable of operating at relatively low speeds, typically under 800 rpm. Such motors, when operated as vehicle traction motors for example, can eliminate the need for both mechanical transmissions and differentials. The motors also have application in servo systems used in robotics and other motion control devices which are gear limited in design.
A need also exists for a low cost, high power electrical generator capable of operating at low speeds, typically under 300 rpm. Such generators may be directly wind-driven by large propellers; they may also be directly driven by water wheels or turbines in streams or dams. It is also contemplated these generators will be able to greatly reduce the need for mechanical gearing, which in typical wind power generation systems can cost more than the generator. Some of these require high efficiency conversion of motive power to electrical power. Rather, the initial cost and the cost of maintenance become the more important factors.
Brushless design of motors requires that stator windings be mounted in a stationary fashion and that rotors be fastened to a shaft for rotary motion. In the past, the stator assembly of a brushless electrical motor has been mounted inside a housing or yoke. The housing or yoke serves no energy conversion function, but it maintains stator alignment and concentricity with the rotor shaft. Elimination of most of the housing would help to realize increased torque-to-weight ratios.
Magnets deliver usable flux in relation to the operating point B.sub.D of the magnets. Magnetic circuits that have flux paths which are always aiding in series with the individual magnet polarities provide a higher operating point B.sub.D than circuits which cause the magnets to be in opposition or which have magnetic flux paths with high reluctance. Further, the greater the flux density per unit mass of magnet, the greater the torque-to-weight ratio will be for the entire machine, other parameters remaining the same.